638 THE VASCULAR SYSTEMS 



and the acromiothoracic and cephalic veins; behind, with the first intercostal space, the corre- 

 sponding Intercostal muscle, the first and second digitations of the Serratus magnus, and the 

 posterior thoracic nerve ; on its outer side, with the brachial plexus, from which it is separated by 

 a little cellular interval; on its inner or thoracic side, with the axillary vein, which overlaps the 

 artery. It is enclosed, together with the axillary vein and the brachial plexus, in a fibrous 

 sheath the axillary sheath continuous above with the cervical fascia. 



RELATIONS OF THE FIRST PORTION OF THE AXILLARY ARTERY. 



In front. 



Pectoralis major. 

 Costocoracoid membrane. 

 External anterior thoracic nerve. 

 Acromiothoracic and cephalic veins. 



Outer side. I Axillary \ Inner side. 



Artery. 



Brachial plexus. y *>* portion. J Axillary vein. 



V. ' 



Behind. 



First Intercostal space and Intercostal muscle. 

 First and Second digitations of Serratus magnus. 

 Posterior thoracic and internal anterior thoracic nerves. 



The second portion is covered, in front, by the Pectoralis major and minor muscles; behind 

 it is the posterior cord of the brachial plexus and some areolar tissue which intervenes between 

 it and the Subscapularis ; on the inner side is the axillary vein, separated from the artery by the 

 inner cord of the brachial plexus and the internal anterior thoracic nerve; on the outer side is 

 the outer cord of the brachial plexus. The brachial plexus of nerves thus surrounds the artery 

 on three sides, and separates it from direct contact with the vein and adjacent muscles. 



RELATIONS OF THE SECOND PORTION OF THE AXILLARY ARTERY. 



In front. 

 Pectoralis major and minor. 



f- \ Inner side. 



Outer side I Axillary \ 



/ Artery. Axillary vein. 



Outer cord of brachial plexus. V ponlon. / Inner cord of brachial plexus. 



X. / Internal anterior thoracic nerve. 



Behind. 

 Subscapularis. 

 Posterior cord of brachial plexus. 



The third portion of the axillary artery extends from the lower border of the Pectoralis 

 minor to the lower border of the tendon of the Teres major. It is in relation, in front, with 

 the lower part of the Pectoralis major above, being covered only by the integument and fascia 

 below; behind, with the lower part of the Subscapularis and the tendons of the Latissimus dorsi 

 and Teres major; on its outer side, with the Coracobrachialis ; on its inner or thoracic side, with 

 the axillary vein. The nerves of the brachial plexus bear the following relation to the artery 

 in this part of its course; on the outer side is the median nerve and the musculocutaneous for a 

 short distance; on the inner side, the ulnar nerve (between the vein and artery) and the lesser 

 internal cutaneous nerve (to the inner side of the vein); in front are the inner head of the median 

 and the internal cutaneous nerve, and behind, the musculospiral and circumflex, the latter 

 extending only as far as the lower border of the Subscapularis muscle. 



